Experimental Determination of Hydrogen-Air Laminar Burning Velocities, and the Effect of Water Mist

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Abstract

This research project characterises an experimental set-up with the aim of
finding laminar burning velocities of premixed hydrogen-air (dry) mixtures,
at initial pressure and pressure of 294 K and 1 bar, using a 20 litre cubic
explosion chamber.
Two different methods were employed; a constant-pressure method (CPM)
applied with a schlieren imaging technique, and a constant-volume method
(CVM) adopting the pressure-time history. Regarding the former method,
linear and non-linear relation between the propagation of flame and stretch
rate was employed to obtain the unstretched flame and burning velocity.
Using the pressure measurements during the transient dispersion process,
CPM using a pressure transducer was employed to calculate the burning
velocity, relating the pressure rise to the radius of the flame.
Both measuring techniques gave laminar burning velocities in agreement,
with a maximum relative difference of 10 %. Observed wrinkling in the flame
propagation due to hydrodynamic instabilities, in addition to limitations
associated with experiments performed in a cubical vessel, made it difficult
to produce quantitative results unison with those found in other literature.
Using a nozzle, hydrogen-air mixtures were introduced to water mist with
concentrations between 0.08-0.3 m^3/kg. This was done to investigate its
influence on the laminar burning velocity. The inclusion of water mist gave
burning velocities increased with as high as 100 %, compared to the dry
results. This was mainly due to the generation of turbulence during the
injection of water mist.